Date: Wed, 22 Sep 2010 17:27:12 -0700 (PDT)
From: Bob Gibson <w5rg@yahoo.com>
Subject: [Amps] filament transformer
I'm looking for a filament transformer for a 3cx3000 or 3cx6000..;My YC156 tube
went south and I can't see paying $450 for a used tube when I can buy a new
tube
for just a little more..so if anyone needs a 15v@15amp filament transformer for
a Yc156 I have one for sale...110 volt..73s Bob
## Beware, the 3x3 is 7.5 V @ 50A . The 3x6 is 7.0 V @ 80A .
## I wound two identical bifilar's, [ each with 10 ga magnet wire, on 8"
long x 1/2" diam
type 43 rod, SSON]. I then paralleled any one winding from 'Rod A'.... with
any one
winding from 'Rod B' and vice versa. This way, you get bifilar action [
opposite current flow]
in each rod. 2 x 10 ga's will easily handle 60A. I initially wind the 10
ga polyimide wire
on .5" OD AL tubing. Then install both AL tunes into amp, bend the stiff
leads, etc, and install
6 ga box lugs, which take 2 x 10 ga wires in parallel nicely. Then u can
fire up the fil and blower
and test the fil. When satisfied, AL tubes are removed, and the fragile,
brittle type 43 rods
are slid down the insides of the winding's. Never wind the 10 ga on the
bare rod itself, it's
brittle enough as is. I found some scrap .5" OD x 8" AL tubing [ old
wilson yagi tips].
This is for a 3CX-3000A7 tube.
## For the 3CX-6000A7 /YU-148 / YC-243 [ socketless 3x6] I used the exact
same procedure,
except that 8 ga magnet wire is used. 2 x 8 ga's in parallel will easily
handle 80A . We used
the same 1/2" Od x 8" long type 43 ferrite rods. Same deal, make 2 x
identical bifilars.
## You would think the uh would drop in 1/2, with two identical windings in
parallel... but it doesn't.
You won't get as many turns with the 8 ga wire, but it has more then plenty of
uh for 160m.
## Ok, here's the kicker. I worked out the maths, 16 ways to sunday...and at
the most, there should only
be a .2 v drop on the 50A 3x3 fil choke. I used TWO lab calibrated
fluke 87's... one on the input to the
fil choke, and one at the socket. I consistently measure .4 v drop. All
connections are rock solid. I checked
teh individual V drop across each connection too, and there is none. Go
figure. The point here is... IF you buy
a 7.5 v @ 50 A fil xfmr.... it will be 7.5V UNDER LOAD of 50A. Since
we lose .4 V in the fil choke.... you
really need a 7.9 v [ under load] fil xfmr. My fil xfmr for the 3x3 amp
was a surplus 8.25 vac @ 79A fil xfmr,
with a 208 vac single phase input. No big deal. I use a small 0-240 vac @
5 A variac anyway.
## same deal with the 3CX-6000A7. To get 7.0 vac at the socket, you really
need 7.4 vac [ UNDER LOAD]
from the fil xfmr. On the 3x6, I use a dahl 7.5 vac @ 75 A fil xfmr [
made for a 4x10] Dahl told me himself,
that you easily suck 80A CCS from his 75A rated xfmr's. Most of the xfmr's
either have taps on the primary,
or folks use a 0-270 vac variac. The point is... to expect to lose .4 vac
across the fil choke.
## on a new/rebuilt 3x3 or 3x6 , we run the fil at RATED voltage, [ measured
at the socket] for 48 hrs...with
just the blower on.. and NO B+. The getter in both tubes is heat activated
from the directly heated cathode.
48 hrs will burn off any residual gas in the tube. Ok, now apply B+ and run
the tube... and leave it at rated fil V for
the nest 150 hrs. !! During the 1st 200 hrs, the emmision wil be
increasing steadily. After 200 hrs, it hits a peak.
OK, at this point [ 200 hrs on your fil hr meter], you reduce the fil V with
the variac, in tiny increments, till the power out
on the PEP meter, [using pulse tuning]...JUST drops off a few watts. Take
note of the exact fil V. THEN increase
the fil v by exactly .1 V Ok now you will get an easy 30,000 hrs out of
the tube.
### To get around the wild V fluctuations I was having for a few yrs, [from
the street, from my neighbour who just got busted
for running a grow op]... I installed a 750 va Sola constant v xfmr. It
outputs a highly regulated 240/120 vac to the input
of the fil variac. Output of variac feeds the input of the fil xfmr. Sola
has it's own dedicated 240 line back to main 200 A panel.
## To meter the fil V.... we installed 100-200 uh chokes [ 100-200ma], one in
each leg..right at the socket. 2 x 22 ga wires
brought to panel, and terminate on some banna plug female test jacks. Before
the wires terminate to the jacks, we install a 500-1000 ohm
ohm, 2 w mof resistor is EACH leg..right at the banana jack. We also install a
.01uf cap from jack to chassis. OK, if jacks
accidently shorted, nothing happens. 7.5 v / 2000 ohms = 3.75 ma = .014 w
per resistor. The pair of resistors will not affect
the fluke 87-A's accuracy either, since it's a high Z dvm. The chokes, one
per leg, at the socket, will keep the drive power out of
the metering circuit. The pair of .01uf caps will kill any residual drive
RF. [ even with 1 kw drive, it doesn't put a dent on a dvm]
## if you want to see pix of all this, contact me off list. Either tube is
a winner. 50 w of drive = 1.5 kw 100 w =2.5 kw
150w = 3.5 kw 200 w = 5.2 kw 700w = 12.5 kw And no 8 min warmup
required, like on a YC-156. Both the 3x3 and 3x6 have a
50 ohm input.
later... Jim VE7RF
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